rickj202

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Hello,

I am interested to hear about everyones building tips and tricks on Cermarks new Viper Jet MKII. I know there have been a couple of build threads in the past but I would like to see and learn what is currently being used. Such as:

What are the best servos to use?
Size of lead extensions?
Turbines size?
What about using BVM E-Z air for the wings?
Do you use air brakes, crow or both?
Are you using the winglets or doing away with them like the full scale one? How does it fly without?
How to elminate adding lead weight to the front for CG?
Any building tips and tricks to make a nice flying jet.

Please add any pictures and suggestions.

Thanks,

Rick

DocYates

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Need to talk to Kevin Greene here on RCU, I know I saw him fly his last week at Blue Grass Jet Jam and it looked like it flew very nicely. I am sure he will be able to give you some good info on the plane and how to set it up.
Tommy

George

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I am getting ready to build one for a friend in a week or so. I built one of the first generation ones for myself over a year and half ago. It is a pretty straight forward build. I did build a tray out into the nose section for ALL the batteries so I would not have to add weight. It worked out perfect for me and I plan on doing the same on this one.

I would suggest using crow on this one. Crow was just beginning to be used on other jets back when I had my Viper and was not very popular as of yet, but proved to be just what the doctor ordered for the ViperJet.

Edit:
Oh yeah, make sure your rudder is SOLID!!!!!

rickj202

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That looks really nice George. What was your overall dry weight?

Thanks,

Rick

George

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Thanks Rick. It has been so long ago, I do not remember the dry weight anymore, but it was right in line with the recommended weight especially since I did not have to add lead to balance.

George

mario tavarez14

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miguel santana from dominican republic have the best viper jet build , you should my contact with him , for pictures he will be glad to email to you

rickj202

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Thanks Mario

Ehab

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Hey Rick; my 2nd generation Viper weighed in at 26 lbs with smoke system and UAT full. It flew great on a P120 at around 200-210 mph. I did not trust the frame above that speed. The winglets are cool but they cause the plane to dance in a cross wind. If you take them off, you have to make a filets to round the wing tips. They fly faster w/o the winglets, but I would not trust it. I used the extra air brake, may be with crow you do not need it. The newest one will come out tail heavy by over a pound and at around 29 lbs. They still fly very nicely and smoothly. I'd recommend gluing the stabs and fin...Call me or Tam for more info.

rickj202

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Hello Ehab,

Why do the winglets cause the plane to dance in cross wind? What is there purpose? Do you remember what servos you used?

Rick

Ehab

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3421 on stabs, 9411 on rudder, 2721 on flaps and ail, 2721 on speed brake.

The winglets on the full size are used to increase fuel efficeincy and reduce tip stall. On the model they looked really nice. It really was not a problem in windy conditions, it just rocked the wings a bit in cross winds. No problem on windy landings.

turn and burn

what landing gear is every one using .

Ehab

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I used Rohm air slim line and a regular nose gear. I think Tam still sells a retract set for the Viper...

rickj202

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Thanks Ehab.

rickj202

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Has anyone done away with the winglets and made it smooth? If so please post pics and how it was done.

Thanks,

Rick

turn and burn

what turbine is every one using as mine has just turned up

P. Richards

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Hey Rick the Viperjet is a scale jet and im sure most of the people that bought the kit left it that way, it was the MB339 that has tip tanks and some do not maybe that is what your looking for...

P. Richards aka Swat Team

rickj202

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Hello Richard,

Correct it is a scale Jet and I love scale planes. The new full size Viper Jet now does not have winglet, hence my questions about doing away with them. What is your opinion?

Thanks,

Rick

c/f

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My Viperjet is 23lbs dry with a Pegasus HP dry.

I used robart 630 and robostruts. Flies like a true pattern ship. 3421 on elevators/Rudder/ailerons with mechanical advantages of 1.25" horns and 5/8" arm. puts torq over 100oz on 5VDC regulated powerbox. 4721 on flaps.

I made custom stainless steel c/g hangars that sandwich in between wing and fuse for hanging of c/g balance.

It is extremely linear on elevator at 200MPH eagle tree indication and landing speeds to full 3 point stall using crow.

I have no ballast and everthing is custom made of carbon fibre to make balance, Did I say NO BALLAST weight was added

Its my favorite flying Jet to date and is why I flew it so much @ Kentucky Jets 06 for the IronMan trophy and Best civilian Jet Route 66 06.

heres a few pix in a Viper thread of my install








heres a 3 point stall touchdown landing:

rickj202

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How old is your Viper Jet? Is it the newer version? 23LBS. dry is very lite.

Thanks,

Rick

AFTERBURNER1

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Just leave em on Rickey Boy!!!! You won't fly the thing anyway. Just keep draggin out that 16 of yours and have a good time!!!!! "SEEN IT"!!!!!!!!!

Ehab

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The peggy HP is over two lbs heavier than a P120. You must have had a very light Viper and used some extra light stuff to keep it at 23 lbs!!! Mine came in at 26 lbs using an accurate lab quaity scale (down to a 1/2 oz accuracy).

Edited for spelling!

P. Richards

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Can you post a shot of the new Viper Jet? I have always been a fan of that airplane...

P. Richards aka Swat Team

rickj202

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Here is a picture of the full scale Viper Jet without the winglets. I am interested in bulding my next Viper jet without as well and would like to know how it would perform.


http://image.rcuniverse.com/forum/up...26/Ge95639.jpg

Kevin Greene

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My setup is not that much different from some of the others that have been successful...Ailerons and Elevators are Hitec 5645 digitals..Flaps are a JR 4721's---If I had it to do over again I would install JR 2721's on the flaps instead of the 4721's as they have metal gears. I've bumped the flap and have stripped a gear..Rudder is a JR 2721..

Since rudder flutter has been an issue in the past I decided to balance the rudder in the rudder counter balance...Absolutely no problems so far...But I did have to add some lead to the nose to compensate for the added weight in the tail.

Landing gear---I modified the gear mounts to take Robart 630's as this is what I had on hand. The struts I had to cut to length myself and find the right strut spring rate---Not a problem if you have done this before. Wheels and brakes are all BVM from the small Sabre.

When you get the CG right the model will need absolutely no elevator trim what so ever...I use crow on landing---Definately helps slow the plane down makes it more stable. Hinge the flaps so that you can get max deflection...For takeoff I use about 20 degrees of flap...

One thing that I have noticed is that if you try to horse the plane off of the runway before sufficient air speed is gathered the model can tip stall...Also, if you get too slow when landing the model can tip stall---The ViperJet will let you know if the stall is approaching by rocking of the wings...When up to speed the jet is an absolute pleasure to fly!!!---Goes exactly where you point it and is pretty fast...I have a JetCat P-120 in mine and I would not install a turbine with less power...

Hope this is helpfull---Kevin

c/f

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Mine is of the MKII version, bought in 1/1/05, tail feathers seem to be more resin than open air.

I shortened up the tailpipe and fues exit seen in picture. moved the turbine as far forward on stock rails. theres is NO OEM hardware used other than TAMs pipe, and OEM tanks, fittings and hardware of my own lighter weight opptions. I used a gary mueller bypass, this too was a weight savings thing over OEM, cant remember how much though.

I make everything of my own out of carbonfibre to mount things. Use o-ring bands to hold things. The mounting carbon items totaled less that 3 oz. of weight. Dreamworks servo frames for servo mounts Ca'd to skins plus addittional scab of carbon to block in 4 sides to opposite skin as well. Covers are strictly overcoat of white sign vinyl on top of OEM cover hold in place, Look ma no screws.

With 2.75" wheels wore down to 2.5" It is hard to get off grass fieild operations as it reaches terminal velocity max of 55MPH and I must horse it off. It does rock once or twice but gets going in a hurry.

I purposely used 3421 with mechanical advantage of arm to horn lenghts (With 5/8" on arm and 1.25" on BVM carbon horns this I believe is in the 100+oz range on 5VDC) All this to keep weight out of tail, The fuel pump is within a 1/8" of the nose, with two 5 cell 1400 packs and a 3000MAH pack for ECU all within the nose cone and servicable access from nose removal. Heck buy cutting off the nose of fuse to a mere bulkead was probably 3oz savings in all the epoxy excess.

Some other items of weight savings is to use 7 day cure urethane imperviess to gas and oil to secure fuel tanks in position. I also make my own twisted leads of exacting lengths, fewer plugs and use shared common and plus wire for dual elevators. Use micro HS 85MG servos for retracts and brakes, Left off rear fuse strakes, This is just a small list of ways I used to save weight, I'm pretty anal to build lighter without sacrifice, just do more with less.

I think the OEM balance is perfect and critical, thats why I made stainless steel hangar sandwich in between wing and fuse and hoist it up on pulleys to insure spot on c/g OEM spot on. I'd willingly send them out to ViperJet owners to hoist theirs up to test.

All my throws are per manual, and I was worried about the elevator as the mechanical advantage I used has full 100% ATV, but it is the most linear elevator response with no need for dual rates or more than 25 digits expo for stick interaction.

I think it paid off as this is my favorite jet to fly currently out of a fleet of Bobcat, Kingcat, Rafaele, MB339.